The present invention pertains generally to an industrial robot, and more particularly, to an apparatus for conveying heavy workpieces using a ceiling-suspended industrial robot.
Japanese Unexamined Patent Publication No. 60-9691 discloses an industrial robot, itself having a relatively small weight, which is adapted for moving more heavy workpieces suspended from a ceiling. In this robot, a balancer or the like having an elastic member such as a spring is employed to apply an upward force to the suspended workpiece.
An example of such a robot is illustrated in FIG. 1 of the drawings. As shown in FIG. 1, a robot 1 is mounted on a floor. The robot 1, a column 1a, an arm 1b, a gripper 2, etc., are operated in response to commands received from a control apparatus (not shown). In performing operations on a workpiece 4 disposed upon a work table 3, it is often necessary to exchange work tools 5 and 6 in switching between work steps. With this arrangement, even if the weight of the tools 5 and 6 exceeds the weight of the robot, the exchange of the tools can be smoothly effectd due to the operation of balancers 7 provided between the ceiling and the objects suspended therefrom, namely, the tools 5 and 6.
However, in this apparatus, there have been problems in that, although the load on the robot is reduced with the use of the balancers 7, a load exceeding the maximum permissible value may be applied to rotary portions of the robot during turning operations of the arm 1b or any rotating operation of the gripper 2. In such a case, an accident may occur due to wear, bending, or the like, and the service life of the robot 1 may be shortened.
More specifically, wires 8 and 9 for supporting the work tools 5 and 6 through the balancer 7 are fixed at their upper ends from the ceiling 10. However, bacause the upper ends of the wires 8 are fixed to the ceiling 10, specifically, at support points 11, when the gripper 2 causes the tool 5 or 6 to move above the workpiece 4 as shown in FIG. 1, the wires 8 and 9 are slantingly stretched. As a result, horizontal forces may be exerted on the gripper 2. Further, this horizontal force may also act on the arm 1b and the column 1a, causing an overload on the robot 1 as a whole.